1. Field of the Invention
The present invention generally relates to test probes for characterizing microwave frequency circuits and packages. More specifically, a variable pitch air coplanar waveguide (CPW) structure allows the pitch of the CPW tips to be adjusted to accommodate a range of pad pitches with minimal degradation in the microwave performance of the probe launch.
2. Description of the Related Art
High performance (e.g. 40 GHz bandwidth) microwave probes are currently available for on-wafer testing of microwave frequency circuits. They are also being used increasingly for package level characterization as well.
These probes are usually constructed of very small diameter micro-coaxial cable which is terminated on the device-under-test (DUT) end in an air coplanar waveguide (CPW) structure in a Ground-Signal-Ground (G-S-G) or similar configuration. A serious disadvantage of these probes is their high cost (in some cases, averaging $600 per probe). Since the CPW tips are fixed in pitch, a different probe needs to be purchased for each significant change in pad pitch or package geometry.